U.S. patent number 5,114,683 [Application Number 07/477,754] was granted by the patent office on 1992-05-19 for thermal decomposition trap.
This patent grant is currently assigned to L'Air Liquide, Societe Anonyme pour l'Etude et l'Exploitation des. Invention is credited to Ikuo Hirase.
United States Patent |
5,114,683 |
Hirase |
May 19, 1992 |
Thermal decomposition trap
Abstract
A thermal decomposition trap includes a trap main body (21)
having an inlet port (26) for supplying a gas to be thermally
decomposed and an outlet port (27) for exhausting the gas, and a
heater (23, 25) for heating the gas supplied in the trap main body
(21). An oil trap (28) containing an oil and having an oil
discharge port (29) and a valve (V3) connected thereto is formed on
a bottom portion of the trap main body (21). Particles generated by
thermal decomposition of the gas are precipitated in the oil in the
oil trap (28). The oil containing the particles is easily
discharged in a short time period by opening the valve (V3) mounted
on the oil discharge port (29). An oil-free auxiliary pump is
arranged between a reaction chamber and the thermal decomposition
trap, whereby a mass flow rate of exhaust from rate in the reaction
chamber is not reduced regardless of the arrangement of the thermal
decomposition trap.
Inventors: |
Hirase; Ikuo (Toride,
JP) |
Assignee: |
L'Air Liquide, Societe Anonyme pour
l'Etude et l'Exploitation des (Paris, FR)
|
Family
ID: |
8202919 |
Appl.
No.: |
07/477,754 |
Filed: |
February 9, 1990 |
Foreign Application Priority Data
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Feb 13, 1989 [EP] |
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89400388.8 |
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Current U.S.
Class: |
422/173; 422/307;
422/310; 55/282.4; 55/300; 55/355 |
Current CPC
Class: |
B01D
53/46 (20130101); B01D 53/72 (20130101); B01D
53/68 (20130101) |
Current International
Class: |
B01D
53/72 (20060101); B01D 53/68 (20060101); B01D
53/46 (20060101); F01N 003/10 () |
Field of
Search: |
;55/355,269,278,300
;422/173,310,307 |
References Cited
[Referenced By]
U.S. Patent Documents
Other References
John Wiley & Sons, New York, 1955, pp. 8-9, C. F. Powell et
al., "Vapor-Plating". .
Journal of Metals JOM, vol. 37, No. 6, Jun. 1985, pp. 63-71,
Warrendale, Pennsylvania, US, M. L. Green et al., "Chemical Vapor
Deposition of Metals for Integrated Circuit Applications"..
|
Primary Examiner: Warden; Robert J.
Assistant Examiner: Santiago; Amalia L.
Attorney, Agent or Firm: Oblon, Spivak, McClelland, Maier
& Neustadt
Claims
I claim:
1. A thermal decomposition trap comprising a trap main body having
an inlet port for supplying a gas to be thermally decomposed and an
outlet port for exhausting the gas, and heating means for heating
the gas supplied in said trap main body, wherein an oil trap
containing an oil and having an oil discharge port and a valve
connected thereto is formed on a bottom portion of said trap main
body; and
wherein a cooling means is located around said oil trap to prevent
evaporation and decomposition of the oil.
2. A trap according to claim 1, wherein said heating means are
located at a central portion of, and around, said trap main
body.
3. A trap according to claim 1, wherein metal mesh plates are
located in said trap main body.
4. A trap according to claim 1, wherein said thermal decomposition
trap has an inert gas supply inlet port.
5. A thermal decomposition apparatus comprising, in serial
connection, a reaction chamber, a thermal decomposition trap for
thermally decomposing a gas from said reaction chamber, and an
oil-free auxiliary pump and a main pump for exhausting said
reaction chamber;
wherein said thermal decomposition trap comprises a trap main body
having an inlet port for supplying a gas to be thermally decomposed
and an outlet port for exhausting the gas, heating means for
heating the gas supplied in said trap main body, and an oil trap,
mounted on a bottom portion of said trap main body containing an
oil, and having an oil discharge port and a valve connected
thereto;
said auxiliary pump is connected to an outlet port of said reaction
chamber and said inlet port of said thermal decomposition trap;
and
said main pump is connected to said outlet portion of said thermal
decomposition trap.
6. An apparatus according to claim 5, wherein said main pump
comprises a rotary pump.
7. An apparatus according to claim 5, wherein said auxiliary pump
comprises a pump selected from the group consisting of a mechanical
booster pump and a turbo molecular pump.
8. An apparatus according to claim 5, wherein an oil trap is
located between said thermal decomposition trap and said main pump.
Description
The present invention relates to a thermal decomposition apparatus
for various compounds and, more particularly, to a thermal
decomposition apparatus comprising an improved thermal
decomposition trap.
Various inorganic halides, inorganic hydrides and organic metal
compounds are widely used as materials for thin film formation by
CVD or the like in a semiconductor manufacturing process. These
compounds have come to be used increasingly in recent years with
the rapid development of the semiconductor industry. These
compounds are supplied in a gaseous state into a reaction chamber
evacuated by a rotary pump to form a thin film. After thin film
formation, any residual non-reacted gas and a by-product of the
reaction are exhausted by the rotary pump.
However, these non-reacted gas and by-product gas of the reaction
react with an oil in the rotary pump when they pass through the
pump, thereby degrading the oil and damaging the pump. In order to
eliminate this drawback, a system is proposed in which a thermal
decomposition trap is arranged before the rotary pump so that the
above gases are flowed through the thermal decomposition trap and
thermally decomposed into substances not reacting with the oil.
FIG. 1 shows an arrangement of such a thermal decomposition
trap.
In the thermal decomposition trap shown in FIG. 1, heater chamber
2, opened to outer atmosphere, for housing heater 3, is inserted
near a central portion of trap main body 1. Main body 1 houses
copper mesh plates 4 so that plates 4 surround chamber 2. Band
heater 5 is wound around main body 1. Inlet port 6 and outlet port
7 are formed in lower and upper portions of main body 1,
respectively.
In the above thermal decomposition trap, a gas from the reaction
chamber is supplied from inlet port 6 in main body 1 and thermally
decomposed on plates 4 heated by heaters 3 and 5. The decomposed
gas is exhausted from outlet port 7 to a rotary pump. Since the
decomposed gas does not react with nor degrade an oil in the rotary
pump, the rotary pump is not damaged.
In the above thermal decomposition trap, however, particles
generated by thermal decomposition of the gases are deposited on
bottom portion 8 of main body 1. Conventionally, the deposited
particles are removed by detaching bottom portion 8 of main body 1
after an operation is stopped. These particles are, however, toxic
and pose a critical problem because they are externally scattered
when they are removed from bottom portion 8 of main body 1.
As shown in FIG. 2, thermal decomposition trap 11 is arranged on
the downstream side immediately after reaction chamber 12, and oil
trap 13, mechanical booster pump 14 and rotary pump 15 are arranged
on its down-stream side. Since the units are arranged in this
manner, a mass flow rate of exhaust from chamber 12 obtained by
pumps 14 and 15 is significantly reduced due to a pressure loss in
trap 11.
It is, therefore, an object of the present invention to provide a
thermal decomposition trap capable of easily removing particles
generated by thermal decomposition of gases from a bottom portion
of a trap main body.
It is another object of the present invention to provide a thermal
decomposition apparatus in which an exhaust rate in a reaction
chamber is not reduced regardless of the arrangement of a thermal
decomposition trap.
According to the present invention, there is provided a thermal
decomposition trap comprising a trap main body having an inlet port
for supplying a gas to be thermally decomposed and an outlet port
for exhausting the gas, and heating means for heating the gas
supplied in the thermal decomposition trap main body, wherein an
oil trap containing an oil and having an oil discharge port and a
valve connected thereto is formed on a bottom portion of the trap
main body.
In the thermal decomposition trap of the present invention, the oil
trap is formed on the bottom portion of the trap main body. An oil,
for example a pump oil, is contained to a predetermined level in
the oil trap. Particles generated by thermal decomposition of the
gas drop into the oil. The valve is mounted on the oil discharge
port formed in the bottom portion of the oil trap. The oil
containing the particles is discharged by opening the valve.
In order to prevent evaporation and decomposition of the oil, it is
preferable to locate a cooling means around the oil trap.
According to the thermal decomposition trap of the present
invention, the particles generated by thermal decomposition of the
gas can be easily removed from the trap in a short time period
while they are kept shielded from outer atmosphere.
In addition, according to the present invention, there is provided
a thermal decomposition apparatus comprising a reaction chamber, a
thermal decomposition trap for thermally decomposing a gas from the
reaction chamber, and an oil-free auxiliary pump and a main pump
for exhausting the reaction chamber, wherein the thermal
decomposition trap comprises a trap main body having an inlet port
for supplying the gas from the reaction chamber and an outlet port
for exhausting the gas, heating means for heating the gas supplied
in the trap main body, and an oil trap, mounted on a bottom portion
of the trap main body, containing an oil, and having an oil
discharge port and a valve connected thereto, the auxiliary pump is
connected to an outlet port of the reaction chamber and the inlet
port of the thermal decomposition trap, and the main pump is
connected to the outlet port of the thermal decomposition trap.
According to the thermal decomposition apparatus of the present
invention, the oil-free auxiliary pump is arranged immediately
after the reaction chamber. Therefore, an exhaust rate in the
reaction chamber is not reduced regardless of the arrangement of
the thermal decomposition trap and can be adjusted without varying
the pressure in the reaction chamber.
Examples of the gas to be decomposed by the thermal decomposition
trap and the thermal decomposition apparatus of the present
invention are inorganic halides such as WF.sub.6, MoF.sub.6 and
TiCl.sub.4 ; organic metal compounds such as Al(C.sub.2
H.sub.5).sub.3, Al(CH.sub.3).sub.3, Al(iC.sub.4 H.sub.9).sub.3,
Zn(C.sub.2 H.sub.5).sub.3, Cd(CH.sub.3).sub.2, In(C.sub.2
H.sub.5).sub.3, Ga(CH.sub.3).sub.3, Ga(C.sub.2 H.sub.5).sub.3,
P(CH.sub.3).sub.3, P(C.sub.2 H.sub.5).sub.3, As(CH.sub.3).sub.3,
As(C.sub.2 H.sub.5).sub.3, B(CH.sub.3).sub.3, B(C.sub.2
H.sub.5).sub.3, Si(CH.sub.3).sub.4, Si(C.sub.2 H.sub.5).sub.4,
Si(OCH.sub.3).sub.4, and Si(OC.sub.2 H.sub.5).sub.4 ; and inorganic
hydrides such as SiH.sub.4, Si.sub.2 H.sub.6 and Si.sub.3
H.sub.8.
BRIEF DESCRIPTION OF THE DRAWINGS
This invention can be more fully understood from the following
detailed description when taken in conjunction with the
accompanying drawings, in which:
FIG. 1 is a sectional view showing a conventional thermal
decomposition trap;
FIG. 2 is a flowchart of a thermal decomposition apparatus adopting
the thermal decomposition trap shown in FIG. 1;
FIG. 3 is a sectional view showing the thermal decomposition trap
according to an embodiment of the present invention; and
FIG. 4 is a flowchart of a thermal decomposition apparatus adopting
the thermal decomposition trap shown in FIG. 3.
An embodiment of the present invention will be described below with
reference to the accompanying drawings.
FIG. 3 is a sectional view showing a thermal decomposition trap
according to an embodiment of the present invention. In the thermal
decomposition trap shown in FIG. 3, heater chamber 22, opened to
outer atmosphere, for housing heater 23, is inserted near a central
portion of trap main body 21. Main body 21 houses metal mesh plates
24, for example made of copper, so that plates 24 surround chamber
22. Band heater 25 is wound around main body 21. Inlet port 26
having valve V1 and outlet port 27 having valve V2 are formed in
lower and upper portions of main body 21. Vibrator 35 is connected
to the upper end of mesh plates 24 by means of vibration
transporting member 36.
Conical oil trap 28 is formed on a bottom portion of main body 21.
Oil discharge port 29 is formed in a bottom portion of oil trap 28,
and valve V3 is mounted on port 29. A predetermined amount of oil
is contained in oil trap 28. In this case, an oil normally used for
a pump is used. Oil trap 28 has oil supply port 30 having valve V4
thereon. The oil is supplied from port 30 in oil trap 28.
Cooling pipe 31 is disposed around oil trap 28, and cooling water
is flowed through pipe 31 to cool the oil in oil trap 28. As a
result, evaporation or thermal decomposition of the oil can be
prevented. Pressure switch 33 for preventing an excessive increase
in pressure in the trap and line 34 for supplying an inert gas such
as nitrogen are mounted on an upper side portion of main body 21.
Valve V5 is mounted on line 34.
In the above thermal decomposition trap, a gas from the reaction
chamber is supplied from inlet port 26 to main body 21 and
thermally decomposed on plates 24 heated by heaters 23 and 25. The
decomposed gas is exhausted from outlet port 27 to the rotary pump.
Particles generated by thermal decomposition fall into the oil in
oil trap 28. Particles attached to the surface of plates 24 can be
easily dropped by actuation of vibrator 35.
When a large amount of particles are deposited in oil trap 28 by a
long-time thermal decomposition, the oil must be exchanged. This
operation is performed as follows.
That is, while valves V1 and V2 are kept closed, valve V5 is opened
to supply nitrogen gas in the trap. The nitrogen gas is supplied
until an atmospheric pressure or the pressure immediately before an
atmospheric pressure is obtained in the trap. Then, valves V3 and
V5 are opened to slowly supply the nitrogen gas to discharge the
oil. Thereafter, valve V3 is closed before the oil in oil trap 28
is completely discharged. Finally, valve V4 is opened to supply a
new oil, thereby completing an oil exchange operation. If
necessary, such an oil exchange operation can be repeated, so that
trap 28 is cleaned.
In this manner, toxic particles generated by thermal decomposition
of the exhaust gas from the reaction chamber can be safely and
easily removed from the trap in a short time period without opening
the trap to expose its interior to the outer atmosphere.
When a W film was actually formed on a silicon wafer by CVD using
WF.sub.6 and hydrogen as a source gas in the reaction chamber, a
gas containing non-reacted WF.sub.6 was exhausted from the reaction
chamber. When the gas was thermally decomposed by the thermal
decomposition trap shown in FIG. 3, particles containing W was
produced as particles. This particles were precipitated in the oil
in oil trap 28 and was easily removed therefrom by the above
operation.
FIG. 4 is a flowchart of a thermal decomposition apparatus adopting
the thermal decomposition trap shown in FIG. 3. In FIG. 4,
mechanical booster pump 44 is arranged on the downstream side
immediately after reaction chamber 42, and thermal decomposition
trap 41, oil trap 43 and rotary pump 45 are arranged on its
downstream side. In this arrangement, since oil-free pump 44 is
arranged on the downstream side immediately after chamber 42, an
exhaust rate in chamber 42 obtained by pumps 44 and 45 is not
reduced due to a pressure loss by trap 41. In addition, the
pressure in the reaction chamber can be adjusted without any
variation.
* * * * *